Tumblr's growth "has been going crazy," and a source tells us that Tumblr has actually spent most of its fundraising time talking to firms that can help it with capacity planning and equipment financing. The startup is about to bring a massive server online, and has plans to light up several more soon.

Briefed on this story, Tumblr president John Maloney told us: "We never talk about the nature of our discussions with financiers."

"Yes, the network continues to scale like crazy and we're always having conversations with firms and smart people who can help with the growth."

Tumblr, founded and run by CEO David Karp, bills itself as "the easiest way to blog." It probably is.

According to Quantcast, the Tumblr blog network has 38 million monthly uniques in the US and more than 90 million worldwide. That is "crazy" growth from a year ago, when the global number was around 10 million.

Here's the chart:

So far in its life, Tumblr has not really tried to figure out how it's going to make money. This has been a smart decision.

With the site scaling with users the way it is, Tumblr would be silly to limit its potential revenues with any actual numbers. Better to leave all that up to the imaginations of its backers.

And truly, if the Tumblr network continues to grow the way it is growing right now for the next couple years, it will suddenly be the size of Facebook – and able to sell ads, water, or anything almost, and make billions. Scale makes that kind of thing easy.

Tumblr is just one of a whole new breed of startups with valuations approaching and surpassing $1 billion. It's all very exciting, but…